1. Field of the Invention
The described embodiments relate to computer systems. More specifically, the described embodiments relate to the distribution of a thermal interface material in a computer system.
2. Related Art
With recent increases in processing speed and reductions in feature sizes, integrated circuit chips (ICs) have begun to consume more power. This has led to a corresponding increase in the operating temperatures of the ICs. Increased operating temperatures can cause inefficient operation, computational errors, or chip failures. Consequently, many ICs include a heat sink that is coupled to the IC to draw heat from the IC. The heat sink maintains lower operating temperatures for the IC, thereby enabling improved operation and longer chip life.
Heat sinks typically have a smooth surface (a “mating surface”) that is placed in contact with the IC and a body that absorbs heat from the IC. Generally, the surface area of the heat sink is significantly larger than the surface area of the IC, thereby providing a larger surface area for dispersing heat generated by the IC. Some heat sinks also include heat dispersion features such as fins, radiators, fans, heat pipes, liquid cooling, phase-change cooling, and/or other features.
The mating surface of a heat sink is typically fabricated with tight tolerances for smoothness (i.e., straightness, levelness, etc.). However, fabricating the heat sink's mating surface so that it is smooth within tolerances of less than dozens of microns is prohibitively expensive. Thus, there are often variations in the smoothness of the heat sink's mating surface. In addition, there may be variations in the smoothness of the mating surface of the IC. These variations in the smoothness can cause significant gaps to occur if the heat sink is used by being placed in contact with the IC. These gaps prevent the heat sink from properly absorbing heat from the affected area of the IC, which can lead to hotspots on the IC, with the attendant risk of damage from overheating and/or uneven heating of the IC. Thus, in most systems, a thermal interface material (TIM) is placed between the heat sink and the IC to provide a heat-conductive interface between the IC and the heat sink. The TIM can fill the gaps between the IC and the heat sink, thereby enabling the heat sink to more effectively draw heat from the IC.
One common form of TIM is a heat-conductive paste or grease that is spread in a layer between the heat sink and the IC. Assembling the heat sink and the IC typically involves placing a drop or dollop of TIM on the IC or heat sink and then pressing the heat sink and the IC together. Under this pressure, the TIM is spread from its initial position to cover the entire mating surface. Unfortunately, certain patterns in the spread of the TIM can result in the TIM being distributed unevenly between the heat sink and the IC. This uneven distribution of TIM can lead to localized hot-spots on the IC, with the attendant risk of damage from overheating and/or uneven heating of the IC.